The field of the invention is camera cranes. Camera cranes are often used in motion picture and television production. The motion picture or television camera is typically mounted on a crane arm supported on a mobile base, dolly, or truck. Camera cranes generally have a crane arm supported on a base, with a camera platform at one end of the arm, and a counter weight at the other end. The crane arm can be pivoted by hand to raise and lower the camera, and also to pan to the left or right side.
Telescoping camera cranes have a telescoping arm that can extend and retract, providing far more capability than fixed length crane arms. U.S. Pat. No. 8,033,742, incorporated herein by reference, describes a camera crane having four telescoping sections providing collective telescoping extension movement of about 60 feet. The camera platform is attached to the front end of the fourth telescoping section, with the crane having a maximum payload of about 230 pounds. The maximum payload rating is determined based on load that the arm can safely support, when the arm is fully telescopically extended and bending moments on the arm are at maximum values. Although in some applications the full 60 feet of telescoping movement may not be needed or used, the maximum payload remains unchanged. Accordingly, it would be advantageous to provide a telescoping crane that can be quickly reconfigured to carry a higher maximum payload.
It is well known that due to changes in the amount of bending deflection of the camera crane arm, as the arm elevation is changed, arm balancing cannot be achieved purely via fixed counterweights. This occurs because the arm is never perfectly straight (unless it is in a purely vertical orientation). Rather, the arm is flexed slightly into an arc, with the most curvature occurring when the arm is horizontal. The centers of gravity of the payload and counterweights therefore change slightly as the elevation angle changes. For example, a camera crane arm may be balanced by adding counterweights during initial set up when the arm is in the horizontal position and bending deflection is at a maximum. However, as the arm is raised to elevate the camera, bending deflection decreases, bringing the arm out of balance and making the arm back-end heavy. Consequently, holding the arm steady then requires significant upward force at the back end of the arm, typically achieved via the crane operators pushing up on the back end of the arm. If the arm is lowered from a balanced horizontal position, the arm becomes back-end light, and requires the crane operators to pull down on the back end of the arm to hold the arm in position. With smaller camera cranes these out-of-balance forces can be compensated for by the crane operator(s). With larger camera cranes however, the out-of-balance forces can make it considerably more difficult to precisely control the crane arm movement and positioning. Accordingly, it is also an object of the invention to provide an improved camera crane arm having a system for better maintaining the camera crane arm in a balanced condition.